Fastening structure including a bolt having a serration that is press-fit into a bolthole of a flange

ABSTRACT

A fastening structure capable of preventing deterioration in the flatness of a surface of a flange portion ( 2 ) when a serration ( 7 ) of a bolt ( 5 ) is press-fit into the flange portion ( 2 ). In this fastening structure, one portion in an axial direction of an outer peripheral surface ( 6 ) of the bolt ( 5 ) is provided with the serration ( 7 ). The bolt ( 5 ) is press-fit into a bolthole ( 3 ) formed through the flange portion ( 2 ) of a mounting member ( 1 ). The serration ( 7 ) is located apart from respective end surfaces ( 2 A) and ( 2 B) of the flange portion ( 2 ) by first and second distances (D, C), and the first and second distances (D, C) each exceed 13% of the thickness (A) of the flange portion ( 2 ). With this arrangement, the serration ( 7 ) presses a bolthole inner peripheral surface ( 13 ) only in the region located far apart from both of the end surfaces ( 2 A and  2 B) of the flange portion ( 2 ).

This is a divisional application of Ser. No. 09/716,220 filed Nov. 21,2000, now U.S. Pat. No. 6,537,007 which is a continuation application ofSer. No. 09/287,185 filed Apr. 6, 1999, which is now U.S. Pat. No.6,174,117.

BACKGROUND OF THE INVENTION

The present invention relates to a fastening structure for fastening abolt to a flange by press-fitting a serration of the bolt into abolthole of the flange.

There has conventionally been a mechanism as shown in FIG. 4, whichadopts this kind of fastening structure. This structure is a structurefor fastening a brake disk 103 and a wheel member 110 to a flange 102 ofan inner ring member 105 by means of a bolt 101 and a nut 111.

According to this fastening structure, the bolt 101 is fixed to theflange 102 by press-fitting a serration 106 formed on the bolt 101 intoa bolthole 107 of the flange 102. Then, the brake disk 103 and the wheelmember 110 are fitted around this bolt 101 and fastened by means of thenut 111.

However, in the aforementioned conventional fastening structure, asshown in FIG. 3, an inner peripheral surface 107A of the bolthole 107 ofthe flange 102 is pressed by the serration 106 when the bolt 101 ispress-fit into the flange 102, so that the flange 102 is elasticallydeformed. Due to this elastic deformation, a flange surface 102A on thebolt head side is deformed into a convex shape, while a flange surface102B on the opposite side is deformed into a concave shape.

As described above, if the flatness of the flange surfaces 102A and 102Bare deteriorated, then the brake disk 103 cannot be mounted parallel tothe flange surface 102B. This leads to the problem that one-sidedabutment of the brake disk 103 is caused, generating vibrations andabnormal noises.

SUMMARY OF THE INVENTION

Accordingly, the object of the present invention is to provide afastening structure capable of preventing the deterioration in flatnessof the flange surface when the serration of the bolt is press-fit intothe flange.

In order to achieve the aforementioned object, the present inventionprovides a fastening structure including a bolt whose one portion in anaxial direction of an outer peripheral surface is provided with aserration is press-fit into a bolthole formed in a flange portion of amounting member.

A first distance between one axial end portion of the serration and oneend surface of the flange portion exceeds 13% of a thickness in theaxial direction of the flange portion, and a second distance between theother axial end portion of the serration and the other end surface ofthe flange portion exceeds 13% of the thickness in the axial directionof the flange portion.

According to the fastening structure of the present invention, theserration is located apart from the respective end surfaces of theflange portion by the first and second distances, and the first andsecond distances each exceed 13% of the thickness of the flange portion.With this arrangement, when the bolt is press-fit into the flangeportion, the serration presses the bolthole inner peripheral surfaceonly in a region far from both the end surfaces of the flange portion(in a region deeper than 13% of the thickness). In the regions close tothe respective end surfaces of the flange portion (in each regionshallower than 13% of the thickness), the serration does not press thebolthole inner peripheral surface.

By thus limiting the region where the serration of the bolt presses thebolthole inner peripheral surface to the region located far apart fromboth the end surfaces of the flange portion, the flange surface can beprevented from deteriorating in flatness when the serration is press-fitinto the flange.

In an embodiment, a center portion in the axial direction of theserration substantially coincides with a center portion in the axialdirection of thickness of the flange portion.

In this embodiment, the center portion in the axial direction of theserration is made to substantially coincide with the center portion inthe direction of thickness of the flange portion. With this arrangement,the dimension in the axial direction of the serration can be maximizedwith the flatness of the flange surface maintained, thereby allowing itsslip torque to be maximized.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given hereinbelow and the accompanying drawingswhich are given by way of illustration only, and thus are not limitativeof the present invention, and wherein:

FIG. 1 is a sectional view showing an embodiment of a fasteningstructure of the present invention;

FIG. 2A is a graph of a characteristic showing a variation in flangeflatness when the serration center position is changed in the aboveembodiment;

FIG. 2B is a graph of a characteristic showing a variation in flangeflatness when the serration end position is changed in the aboveembodiment;

FIG. 3 is a sectional view showing a conventional fastening structure;and

FIG. 4 is a sectional view of an automobile wheel bearing having theconventional fastening structure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be described in detail below on the basis ofthe embodiment thereof with reference to the drawings.

FIG. 1 shows an embodiment of the fastening structure of the presentinvention. In this embodiment, a bolt 5 is press-fit into a bolthole 3formed in a metal flange portion 2 of a mounting member 1. A serration 7is formed on a portion of the bolt in an axial direction of an outerperipheral surface 6 of the bolt 5.

A first distance D between one axial end portion 7A of this serration 7and an end surface 2A on a bolt head 8 side of the flange portion 2occupies 18% of the thickness A in the axial direction of the flangeportion 2. A second distance C between the other axial end portion 7B ofthis serration 7 and the other end surface 2B of the flange portion 2occupies 30% of the above thickness A.

Then, the center portion 10 in the axial direction of this serration 7is made to substantially coincide with the center portion 11 in thedirection of thickness of the flange portion 2.

According to the fastening structure of the above construction, theserration 7 is located apart from both the end surfaces 2A and 2B of theflange portion 2 by the first and second distances D and C, and thefirst and second distances D and C each exceed 13% of the thickness A ofthe flange portion 2. With this arrangement, when the bolt 5 ispress-fit into the flange portion 2, the serration 7 presses thebolthole inner peripheral surface 13 only in a region located far fromboth the end surfaces 2A and 2B of the flange portion 2 (in the region Fdeeper than 13% of the thickness A). In the regions close to both theend surfaces 2A and 2B of the flange portion 2 (in the regions G and Hshallower than 13% of the thickness), the serration 7 does not press thebolthole inner peripheral surface 13.

As described above, by limiting the region where the serration 7 of thebolt 5 presses the bolthole inner peripheral surface 13 to the regionlocated far apart from both the end surfaces 2A and 2B of the flangeportion 2, the flange surfaces 2A and 2B can be prevented fromdeteriorating in flatness when the serration 7 is press-fit into theflange portion 2. Therefore, for example, a brake disk 21 or the likecan be mounted on the flat flange surface 2B, so that the one-sidedabutment of the brake disk 21 or the like can be prevented, and so thatthe generation of vibrations and abnormal noises can be prevented.

The above effects will be described on the basis of a concreteexperimental example. According to this experimental example, aplurality of fastening structure samples in each of which a ratio (%) ofthe second distance C with respect to the thickness A of the flangeportion 2 was set to a specified value within a range of 0% to 30% weresubjected to the measurement of flange flatness. The measurement resultis shown in FIG. 2B. As shown in FIG. 2B, when (C/A)×100% becomes equalto or smaller than 13%, the flatness of the flange surface 2B abruptlydeteriorates. In the region where (C/A)×100% ranges beyond 13% to 30%,the flatness of the flange surface 2B is satisfactory and kept at anapproximately constant value. As described above, by positioning theaxial end portion 7B of the serration 7 apart from the flange surface 2Bby a dimension of 13% or more of the thickness A, the flatness of theflange surface 2B is made satisfactory, thereby allowing the brake disk,21 or the like to be mounted on this flat flange surface 2B. Therefore,the one-sided abutment of the brake disk or the like can be prevented,and the generation of vibrations and abnormal noises can be prevented.

FIG. 2A shows the measurement result of the flange flatness of aplurality of fastening structure samples in each of which a ratio (%) ofa distance B between the center portion 10 of the serration 7 withrespect to the thickness A of the flange portion 2 is set to a specifiedvalue within a range of 30% to 70%. As shown in FIG. 2A, the flangeflatness was the best when (B/A)×100% was 50%, and the flange flatnessexhibited an approximately constant satisfactory value within the rangein which (B/A)×100% ranges from 43% to 57%. In the case where (B/A)×100%was smaller than 43% or greater than 57%, the flange flatnessdeteriorated abruptly, as a result.

In this embodiment, the center portion 10 in the axial direction of theserration 7 was made to substantially coincide with the center portion11 in the direction of thickness of the flange portion 2. Therefore, thefirst and second distances D and C between the respective end portions7A and 7B of the serration 7 and the respective end surfaces 2A and 2Bof the flange portion 2 can be made approximately equal to each other,and accordingly, satisfactory flange flatness can be achieved. Ascompared with a case where the center portion 10 is displaced from thecenter portion 11, a serration having a great dimension in the axialdirection can be arranged in the deep region F, so that the slip torquecan be increased.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

What is claimed is:
 1. A fastening structure comprising: a bolt having abolt head, a larger outer diameter portion extending in an axialdirection of the bolt, a serration provided on an outer peripheralsurface of the larger outer diameter portion, and a smaller outerdiameter portion extending in the axial direction of the bolt andprovided with a thread portion; and a mounting member having a flangeportion in which a bolthole is formed and to which a brake disk is fixedby the bolt passing through the bolthole of the flange portion and ahole of the brake disk, a abutting surface of the bolt head abutting ona seat surface of the flange portion of the mounting member; and whereinthe bolthole of the flange portion is comprised of a first enlarged partenlarged in a taper shape toward the seat surface of the flange portion,a center small diameter part engaged with the serration of the bolt, anda second enlarged part enlarged in a taper shape toward the brake diskside; and wherein the second enlarged part is longer in an axialdirection of the bolthole than the first enlarged part.
 2. A fasteningstructure as claimed in claim 1, wherein all of the serration of thebolt is engaged with the center small diameter part of the bolthole ofthe flange portion.
 3. A fastening structure as claimed in claim 1,wherein the second enlarged part of the bolthole has a length in theaxial direction of the bolt exceeding 13% of a thickness in the axialdirection of the flange portion.
 4. A fastening structure as claimed inclaim 1, wherein a length in the axial direction of the serration of thebolt does not exceed 74% of a thickness in the axial direction of theflange portion.